As an internal combustion engine cooling device, a water-cooled cooling device is generally known, in which cooling water is circulated in a water jacket formed in a cylinder block and a cylinder head to cool the cylinder block and the cylinder head. Such a water-cooled cooling device is generally configured of a pump, a water jacket, a radiator, a cooling water passage connecting the water jacket to the radiator, and a thermostat for adjusting the flow rate of the cooling water introduced into the radiator.
In recent years, a pump such as an electric pump, which is capable of changing the discharge performance without depending on the engine operating state has been put to practical use as a pump for circulating cooling water. For example, a cooling device described in Patent Document 1 adopts such an electric pump, and halts the operation of the pump until the cooling water temperature reaches a predetermined temperature at activation of the engine and the like, thereby halting circulation of the cooling water, thereby promoting warm-up.
In such a cooling device, when the cooling water temperature exceeds the predetermined temperature and warm-up proceeds to some extent, the electric pump is activated to start circulation of the cooling water. After start of circulation of the cooling water, when the cooling water temperature further rises, the thermostat is opened and the cooling water begins to be introduced into the radiator. As a result, heat of the cooling water is radiated to the outside by the radiator, and the heat-radiation amount and the heat-absorption amount absorbed by the cooling water through engine combustion achieve a state of equilibrium. Thus, the cooling water temperature is kept substantially constant and the temperature of the internal combustion engine is also kept at a proper temperature in operation.